This invention relates to a dimmer unit for controlling the power supplied to a lamp.
Conventional dimmer units are provided as a replacement light switch which controls the power supplied to the light socket associated with the switch, depending upon the dimmer setting. Typically, such a unit uses a triac for the power control.
A problem with this system is that a new light switch must be wired into place, which is inconvenient for tan ed user. Furthermore, the multiple light switches are associated with an individual light socket, for example in hallways and landings, the use of dimmer switches is more complicated.
According to the invention, there is provided a dimmer unit for controlling the power supplied to a lamp, the unit being adapted for connection to a light socket and comprising:
means for providing a varying output signal during a brightness selection cycle which is initiated by supplying power to the dimmer unit; and
means for storing a value representing a selected brightness at termination of the brightness selection cycle, the brightness selection cycle being terminated by ceasing the supply of power to the dimmer unit.
The dimmer unit of the invention is associated with a light socket, so that no wiring is required. The dimmer unit may either be provided as a separate component for insertion between the lamp and the light socket, or else it may be provided in the lamp itself.
The varying output signal preferably comprises the brightness of the lamp, and the dimmer unit then comprises means for ramping the power supplied to the lamp during the brightness selection cycle. Other output signals may be contemplated, for example a varying audible signal.
The brightness selection cycle is terminated by switching off the power to the unit. This is thereby achieved using the conventional light switch. When power is net applied to the dimmer unit, it provides power to the lamp corresponding to the selected brightness. Even when applying power corresponding to the selected brightness, the power may again be ramped, so as to limit the thermal shock of the lamp and prolong its lifetime.
The means for storing a value may comprise a non-volatile memory, so that no power is required by the dimmer unit when there is no power supplied to the light socket. Alternatively, normal processor memory may be used, and power may be maintained to the memory by a capacitor arrangement. The construction of the dimmer unit can then be as simple and cost effective as possible, permitting the induction of the unit into the lamp itself.
The ramping of power supplied to the lamp makes this more feasible, as it prolongs the lifetime of the lamp.
The means for ramping power preferably comprises a controller for controlling a triac which governs the power supplied to the lamp. Of course, other electronic switches my also be used.
The dimmer unit may also provide a security mode. For this purpose, the unit may comprise means for determining whether the the during which power is applied to the unit is below a threshold time period, and for switching the unit to a security mode if power is applied for less than the threshold time period after setting a brightness level.
In order to set a brightness level the unit must be turned on and off with a short enough delay that the lamp has not reached fill brightness. Furthermore, to initialise the security mode, the dimmer unit must again be turned on and off with a delay below the threshold time period. Therefore, to activate the security mode the dimmer unit must be turned on and off twice in succession.
For the security mode, the dimmer unit preferably comprises a tight detector for controlling the supply of power to the lamp during the security mode.
The unit may further comprise a sensor enabling the brightness selection cycle to be started and terminated remotely without interrupting the powersupply to the dimmer unit. This may enable an infrared remote control to be implemented or a sound activated system, as additional functionality when the dimmer unit is turned on.
The invention also provides a method of selecting a dimmer unit setting corresponding to a brightness of a lamp associated with the dimmer unit, the dimmer unit being adapted for connection to a light socket, the method comprising:
(i) supplying power to the unit by switching on power to the light socket, the dimmer unit ramping the power supplied to the lamp;
(ii) switching off power to the light socket to select the brightness reached, the dimmer unit storing a value representing the selected brightness; and
(iii) switching on power to the light socket, the dimmer unit then applying power to the lamp corresponding to the selected brightness.